A number of attempts have been made to provide a simple, reliable chair and control which allows the chair to move in tune with the user's movement, and also alleviate the problem of "shirt pull" found in many conventional chairs. "Shirt pull" occurs in chairs which, when a user tilts the chair rearwardly, the chair back moves longitudinally up the user's back, pulling up the user's shirt from its normal retention at the waist.
An additional problem occurs in chairs in which the back and seat tilt at substantially the same rate, that is, where the degree of back tilt and seat tilt are substantially the same. In such chairs, as the user leans back, the front portion of the seat exerts upward force on the back of the user's upper legs which can be uncomfortable and even impair blood circulation through the user's legs. Furthermore, if too much of the user's weight is shifted backward, the user can lose stability.
It is therefore desirable to have a chair in which the back and seat tilt separately. More particularly, it is desirable to have a chair in which, as the user leans back, the degree of back tilt is significantly greater than the degree of seat tilt.
It is also desirable that the seat provide independent flexibility of support for the user, particularly at the front portion of the seat, to further accommodate the user in various typical body positions. The seat should accommodate, for example, the user shifting left and right, straightening one leg more than the other, or extending both legs, without putting undue localized pressure on the user's legs. To these ends, the seat should allow torsional (left-right) flexing of the front portion of the seat, as well as vertical resilience of the front portion for fore-and-aft pitch flexibility.
Further it is desirable to provide a finished, integrated and smooth surfaced pedestal and support structure.
While chairs have been proposed previously toward accomplishing the various noted characteristics, it is desirable to obtain improved designs which provide these desirable characteristics in an efficacious manner and which can be produced economically.
The present invention achieves differential tilt, that is, a greater degree of back tilt to seat tilt, in a chair having separate back and seat supports. The chair control mechanism is designed to allow for movement of the chair back and seat in concert with the user's natural body seating and semi-reclining movements, while alleviating the problem known as "shirt pull" found in many prior art chairs. It also provides both torsional and vertical yieldability of the front portion of the seat to further comfortably accommodate various typical user body positions.
A further advantage of the preferred embodiment as illustrated is that it can be economically manufactured by modifying existing chair tilt control mechanisms, e.g., a known control available from Faultless Caster of Evansville, Ind.